Fixture: Legacy JSX Runtimes (#20012)

* Fixture: Legacy JSX Runtimes

* Add more comments

fixtures/legacy-jsx-runtimes/README.md

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+# Legacy JSX Runtimes
+
+This is an internal testing fixture for the special JSX runtime versions released for 0.14, 15, and 16.
+
+They are checked into the corresponding `react-*/cjs/*` folders.
+
+Run the full regression suite:
+
+```
+yarn
+yarn test
+```

fixtures/legacy-jsx-runtimes/babel.config.js

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+module.exports = {
+  presets: [
+    [
+      '@babel/react',
+      {
+        runtime: 'automatic',
+        development: process.env.BABEL_ENV === 'development',
+      },
+    ],
+  ],
+  plugins: ['@babel/plugin-transform-modules-commonjs'],
+};

fixtures/legacy-jsx-runtimes/lint-runtimes.js

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+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @emails react-core
+ */
+
+'use strict';
+
+const path = require('path');
+
+const {ESLint} = require('eslint');
+
+function getESLintInstance(format) {
+  return new ESLint({
+    useEslintrc: false,
+    overrideConfigFile:
+      __dirname + `../../../scripts/rollup/validate/eslintrc.${format}.js`,
+    ignore: false,
+  });
+}
+
+const esLints = {
+  cjs: getESLintInstance('cjs'),
+};
+
+// Performs sanity checks on bundles *built* by Rollup.
+// Helps catch Rollup regressions.
+async function lint(folder) {
+  console.log(`Linting ` + folder);
+  const eslint = esLints.cjs;
+
+  const results = await eslint.lintFiles([
+    __dirname + '/' + folder + '/cjs/react-jsx-dev-runtime.development.js',
+    __dirname + '/' + folder + '/cjs/react-jsx-dev-runtime.production.min.js',
+    __dirname + '/' + folder + '/cjs/react-jsx-runtime.development.js',
+    __dirname + '/' + folder + '/cjs/react-jsx-runtime.production.min.js',
+  ]);
+  if (
+    results.some(result => result.errorCount > 0 || result.warningCount > 0)
+  ) {
+    process.exitCode = 1;
+    console.log(`Failed`);
+    const formatter = await eslint.loadFormatter('stylish');
+    const resultText = formatter.format(results);
+    console.log(resultText);
+  }
+}
+
+async function lintEverything() {
+  console.log(`Linting known bundles...`);
+  await lint('react-14');
+  await lint('react-15');
+  await lint('react-16');
+  await lint('react-17');
+}
+
+lintEverything().catch(error => {
+  process.exitCode = 1;
+  console.error(error);
+});

fixtures/legacy-jsx-runtimes/package.json

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+{
+  "dependencies": {
+    "@babel/plugin-transform-modules-commonjs": "^7.10.4",
+    "@babel/preset-react": "^7.10.4",
+    "jest": "^26.5.3"
+  },
+  "jest": {
+    "setupFilesAfterEnv": ["./setupTests.js"]
+  },
+  "scripts": {
+    "install-all": "cd react-14 && yarn && cd ../react-15 && yarn && cd ../react-16 && yarn && cd ../react-17 && yarn && cd ..",
+    "lint": "node lint-runtimes.js",
+    "pretest": "yarn install-all && yarn lint",
+    "test-jsxdev-dev": "BABEL_ENV=development NODE_ENV=development jest",
+    "test-jsx-dev": "BABEL_ENV=production NODE_ENV=development jest",
+    "test-jsx-prod": "BABEL_ENV=production NODE_ENV=production jest",
+    "test": "yarn test-jsxdev-dev && yarn test-jsx-dev && yarn test-jsx-prod"
+  }
+}